8. Hacksaws and Their Use

For efficient use of a hacksaw, the following points should be observed:

• Hold the hacksaw with the handle in one hand, the other hand gripping the front of the frame.

• Hold the saw perpendicular to the metal.

• Position the metal in the vice so that the saw cut is vertical.

• Support the metal close to the saw cut.

• Start the saw cut at a low angle on the far edge of the metal.

• Saw at less than one stroke per second.

• Avoid undue twisting of the blade.

• Use the whole length of the blade.

• Avoid using a new blade in an old saw cut.

There are various types of hacksaw blade.

Flexible blades made from high carbon tool steel: These have the teeth

hardened but the back of the blade remains soft so that the blades are relatively tough.

• Flexible blades made from high speed steel: These are more expensive but will last longer and cut harder metals.

• All hard blades made from high speed steel: These are hardened throughout and require more careful handling to avoid breakage.

Blades are obtainable in two lengths – 250 and 300 mm. Hacksaw frames are usually adjustable to take the different lengths of blade.

The grade of a hacksaw blade refers to the number of teeth. Commonly used grades are 18T, 24T and 32T (teeth per 25 mm), although some manufacturers specify the grade by the pitch (distance between consecutive teeth) in millimetres.

Selection of the correct grade: As a general guide, use a fine toothed blade for thin metal or tubing and a coarse toothed blade for heavy section work. A too coarse blade cutting thin metal will result in teeth being broken from the blade. At least three teeth should be in contact with the metal at all times.

The teeth are 'set' (bent to either side) so that the blade will cut a saw kerf greater than the thickness of the blade. As the blade wears, the teeth become worn on the outside and consequently the saw cut is narrower. It is for this reason that a new saw blade should not be used to complete a cut made by an old, worn blade.

• Select the correct grade of blade for the job in hand.

• Fit the blade over the pins, ensuring that the teeth are pointing forward so that the blade will cut on the forward stroke.

• Tension the blade using finger pressure only on the tightening screw.

Although the depth of saw cut is limited by the distance from the blade to the frame, if a long cut is required along the edge of a piece of metal, the blade may be rotated through 90° to allow the frame to clear the metal.